Punishment is pointless if you cannot expect anyone (who could potentially commit a certain undesirable act) to ever realise any connection between the undesirable act and its punishment. This seems to me to be the case in this scenario as described, so pre-punishing Hitler would be a waste of resources.
If we, however, imagine that we're living in the future, and the Time Travel Licensing Agency has declared it legal to go around vexating would-be serious criminals, then stealing Hitler's wallet and publishing the fact would help increase the impact of the TTLA's deterrent. But this is really a scenario where time travelling doesn't add anything interesting to the idea.
(Small aside: I'd replace stealing Hitler's wallet with, say, slashing his bike tires, to more effectively take the issue of guilt-free personal profit out of the equation without invoking the "you don't need the money" clause.)
Well, if having many time-travelers pre-punishing crimes is useful, then presumably having a single time-traveler pre-punish one crime is worth some fraction of that utility.
Here's an edited version of a puzzle from the book "Chuck Klosterman four" by Chuck Klosterman.
When should you punish someone for a crime they will commit in the future? Discuss.